The invention relates to a fuel-injection diesel internal-combustion engine having an injection pump which, with respect to the delivery quantity, the delivery pressure and/or the delivery time, is controlled as a function of the load and/or the rotational speed. An injection nozzle is connected in the feed line to the delivery side of the pump and, by way of at least one injection opening, leads out to a combustion space of the internal-combustion engine. The injection opening can be closed by way of a nozzle needle which, in the opening direction, can be displaced by way of the fuel delivered on the delivery side by the pump and is loaded in the closing direction by way of a pressure spring. The pressure spring is arranged in a closed no-discharge spring chamber which is connected with the delivery side of the pump by way of a throttling point which is formed by a sliding guide for the nozzle needle. The sliding guide, in addition to being loaded by the pressure spring, is loaded in the closing direction by way of the fuel pressure existing in the spring chamber filled with fuel. The fuel pressure existing in the spring chamber is variable and is a function of the control position of the injection pump corresponding to the defined driving condition.
Fuel-injection diesel internal-combustion engines are known from German Patent Document DE 31 29 916 A1. In the inflow of the nozzle connected to the delivery side of the pump, a constant-volume relief pressure valve is provided on the pump outlet side. A force of the pressure spring is experimentally determined for a defined internal-combustion engine and a defined rotational speed and load range of this internal-combustion engine, at which force, in the stabilized condition of the internal-combustion engine, at an arbitrary point of its working regime, a constant cycle delivery quantity, that is, injection quantity is to be ensured. This is the result of the fact that, relative to this working point, the residual pressure in the feed line to the nozzle as well as the residual pressure in the spring chamber are held at the same level.
In the fuel-injection diesel internal-combustion engines of the initially mentioned type, the phenomenon is to be countered that, under stabilized conditions, there is usually a progressive increase of the residual pressure in the feed line from the pump to the nozzle and in the spring chamber. As a result, while the control position of the injection pump is the same, the amount of the injection quantity will gradually fall until there will finally be a blocking of the injection valve by the fuel pressure in the spring chamber and therefore a reduction of the injection quantity to zero.
In contrast, by means of the known solution, the residual pressure in the spring chamber and in the feed line from the pump to the nozzle is to be maintained at the same level so that a constant injection quantity is ensured for a working point.
According to the invention, the above-described effect, which causes the internal-combustion engine to die due to the lack of a fuel supply, is to be avoided over the whole working range of the engine and therefore a corresponding injection system for internal-combustion engines of motor vehicles is to be utilized which can be used over the whole working range.
This is achieved by the invention in that a rise of the pressure in the spring chamber is to be countered by way of an operating pressure corresponding for a defined driving condition to the control position of the injection pump by increasing the delivery time of the pump. If the delivery time is increased, a higher delivery pressure is obtained which the pressure in the spring chamber constructed as the pressure chamber can follow only in a delayed manner because of the throttling point situated in the connection to the spring chamber, in which case the pressure level will also fall. Correspondingly, by means of the measure according to the invention, the fuel supply of the combustion space of the internal-combustion engine, which is tendentiously reduced by the pressure buildup in the spring chamber, can be compensated and the operation of the internal-combustion engine can be maintained in an undisturbed manner.
The solution according to the invention is particularly important for diesel internal-combustion engines in whose fuel injection high pump pressures and correspondingly high injection pressures are used. For example, in systems without any pipe connection between the pump and the nozzle, which are known as pump-nozzle elements, as well as in systems operating with plug-type pumps, a so-called plug-type pump is located adjacent to the nozzle assigned to the respective combustion space. The plug-type pump is acted upon by way of the cam of a camshaft. In comparison to systems which operate with distributor pumps or in-line injection pumps, very short pipe paths are obtained and therefore advantageous conditions for the work with high injection pressures. High injection pressures are those pressures which are in the range of 1,700 bar, in which case in corresponding systems injection opening pressures of up to 350 bar are used.
If work takes place with such high pressures, very high stress occurs with respect to the nozzles and high spring forces must also be applied in order to achieve corresponding closing forces for the nozzle needle. The high closing and opening forces acting upon the nozzle needle make such systems particularly sensitive to vibrations and these vibrations result in considerable problems concerning noise and wear. The wear problems are partially also indirect because vibrations of the nozzle needle promote the blowing back of burnable gases through the injection opening into the nozzle and thus the coking of the nozzle.
Since the addressed pressures represent peak pressures, significantly lower pump delivery and injection pressures occur for other operating phases of the internal-combustion engine. Nevertheless, a fuel injection diesel internal-combustion engine constructed according to the invention must, in particular, also meet the requirement that it exhibit a correspondingly cultivated running in the idling operation. The invention definitely meets these requirements.
According to the invention, the force of the pressure spring loading the nozzle needle in the closing direction does not have to be designed for the maximal pressures to be controlled but can be selected to be lower. As the result of the no-discharge design of the spring chamber, which is therefore closed with the exception of the opening for the nozzle needle, a pressure builds up in the spring chamber which is superimposed on the spring pressure and is added to it. Since, in addition, this pressure is a function of the respective working pressure of the pump system, an adaptation of the closing pressure acting upon the nozzle needle to the respective pump or injection pressure can be achieved. If the closing pressure must be applied only by the pressure spring, this pressure spring must be designed for the maximal pump or injection pressure as the working pressure; a corresponding adaptation possibility does not exist.
The closed spring chamber acting as the pressure chamber has the result that, during the opening of the nozzle needle by the compression of the fuel in the spring chamber, an additional pressure rise will occur. Since the connection to the spring chamber is constructed as a throttling point, this pressure rise is at least partially compensated by a certain expansion by way of the throttling point, which leads to a damping of vibrations. The result is a stable injection and a lower wear of the nozzle.
Another damping influence can be achieved in that the spring chamber--pressure spring system is, in addition, constructed as a vibration damper. This is achieved by the fact that the pressure spring is radially largely arranged without contact, thus without any significant play with respect to the spring chamber. In the case of such an arrangement, the fuel between the pressure spring and the wall of the spring chamber forms virtually only a film, and damping effects therefore occur because of the occurring fluid friction.
The rising of the pressure in the spring chamber can be detected within the scope of the solution according to the invention directly as well as indirectly, in which case an indirect detection is possible, for example, by way of the rotational speed, the opening point in time of the nozzle needle, the injection time and/or the closing point in time of the nozzle needle.
Because of the increase of the delivery time in the spring chamber, the pressure in the spring chamber can be raised with respect to a limit value to which a closing force corresponds which is exercised on the nozzle needle and which is lower than the increased opening force resulting in connection with the increase of the delivery time.
On the whole, an internal-combustion engine operating with a fuel injection according to the invention is distinguished by a simplified construction because the pump-nozzle system in the connection between the pump and the nozzle can be constructed without valves. Thus, the invention does not require constant pressure relief pressure valves or constant volume pressure relief pressure valves. Furthermore, the invention permits, while high and highest injection pressures are controlled, relatively low opening pressures, not least because of the fuel injection stabilized by the avoidance of vibrations. All this results in a perfect noise behavior, particularly also during idling and in the low partial-load range.